profound

pruh-FOUND

meaning in plain English

the deep part of the sea or ocean, far down where you cannot see the bottom

Picture a deep sea trench—its mystery is profound, like thoughts that sink far below the surface.

for example

The researchers set their instruments in the profound to study the strange creatures living there.

If you stand on a boat and look out over the profound, you see a huge, dark water that seems endless, because it goes down far beyond what you can see.